Method for forming thin film, substrate having transparent electroconductive film and photoelectric conversion device using the substrate

ABSTRACT

The present invention provides a thin film-forming method by which, even when a thin film containing a crystalline metal oxide as the main component is formed over a wide area within a short time utilizing a thermal decomposition method, the thickness of the thin film becomes relatively uniform. A thin film-forming method of the present invention includes forming a thin film using a raw material containing a chloride of a metal, and prior to the forming of the thin film, 1) disposing metal-containing particles on the substrate, or 2) forming, at a film deposition rate slower than a film deposition rate for the thin film, a metal-containing thin film on the substrate, and wherein, in the case of the step 2), the thin film containing the metal oxide as the main component is directly formed on the metal-containing thin film.

TECHNICAL FIELD

This invention relates to a method of forming, on a substrate such asglass, a thin film containing a crystalline metal oxide as the maincomponent using a chloride of a metal as a raw material, by a thermaldecomposition method. The invention further relates to a substrate inwhich the thin film containing a crystalline metal oxide as the maincomponent functions as a transparent conductive film, and to aphotoelectric conversion element using the substrate.

BACKGROUND ART

A thin film containing a metal oxide such as tin oxide has the functionof reflecting infrared rays. Since a glass sheet provided with this thinfilm reduces the total solar energy transmittance and does not allow theheat within rooms to escape to the outdoors, it is widely available inthe market as a low-emissivity glass. This thin film also can exhibitthe function of shielding electromagnetic waves. A known method formanufacturing a glass sheet of this kind is such that a thin film of ametallic compound is formed on a high temperature glass surfaceutilizing thermal decomposition methods, such as a chemical vapordeposition method (CVD method) and a spraying method in which a solutionmaterial or a solid material is sprayed.

For example, JP 11(1999)-509895 A describes a method of forming a thinfilm of a tin oxide by supplying a gaseous reaction mixture containingan organic tin compound, hydrogen fluoride, oxygen, and water onto ahigh temperature glass surface. JP 6(1994)-47482 B describes a method offorming a thin film comprising a tin oxide by supplying a vapor of anorganic tin compound on a glass ribbon surface in a float bath in afloat manufacturing process. The use of the organic tin compounds suchas described in these patent publications as a raw material for a thinfilm has an advantage that the thickness of the thin film easily is madeuniform. Nevertheless, because organic tin compounds have highenvironmental loads as with tributyltin compounds, the use ofalternative raw materials that replace organic tin compounds has beendesired in recent years.

Meanwhile, tin chloride conventionally has been used widely as a rawmaterial for a tin oxide thin film in thermal decomposition methods. Forexample, JP 2(1990)-175631 A describes a method of forming a coatingfilm in which, with a CVD method, a first flow of tin tetrachloride anda second flow of water vapor are supplied onto a glass with a turbulentflow. Also, JP 9(1997)-40442 A describes a method of depositing a tinoxide thin film uniformly by a CVD method, in which tin tetrachlorideand water are pre-mixed and supplied onto a glass substrate with alaminar flow.

Such methods of forming a thin film containing a metal oxide thatutilize thermal decomposition methods are inferior to physical vapordeposition methods, such as a sputtering method, in that it is difficultto obtain a uniform film thickness; nevertheless, they are capable offorming a thin film over a wide area within a short time at a relativelyuniform thickness and therefore are suitable for mass production ofindustrial products. With the thermal decomposition methods, generally,the higher the temperature of the reaction system is, the faster thefilm deposition rate, although the situations vary somewhat depending onthe compositional components of the raw materials for the thin film.Accordingly, it seems that higher temperatures are preferable for theformation of a thin film in industrial production processes.

With the background of recent energy issues and environmental issues,solar cells have attracted attention. There are various types of solarcells, and among them, thin film solar cells have been considered as themainstream henceforth in terms of resource savings. A generalconfiguration of thin film solar cell is as follows. The structure isthat a transparent conductive film composed of tin oxide (SnO₂) or thelike, a photoelectric conversion layer composed of a non-crystallinesemiconductor such as amorphous silicon or amorphous silicon germanium,and a conductive film are stacked successively on a transparentsubstrate such as a glass sheet.

Solar cells constantly have been required to improve their photoelectricconversion efficiency, and various technologies have been developed andput into practical use for that purpose. A typical example is atechnology for producing a so-called light trapping effect, in which thesurface of a transparent conductive film is provided with surfaceroughness where incident light is scattered to lengthen the optical pathlength in the photoelectric conversion layer. Such surface roughness inthe transparent conductive film is originated from crystal growth of tinoxide. In order to grow large crystal grains of tin oxide, it iseffective to carry out a film deposition at high temperatures or toincrease the thickness of the thin film. For example, JP 2862174 Bdescribes an electrically-conductive film solar cell substrate that isformed by atmospheric-pressure chemical vapor deposition using SnCl₄,H₂O, CH₃OH, and HF as raw materials, with numerous protrusions on thesurface.

In addition, in order to enhance the photoelectric conversion efficiencyof a solar cell, it is essential to increase the amount of lightincident on the photoelectric conversion layer, and there have beendeveloped a technology for reducing the reflectance for incident lightand a technology for reducing the absorptance in the transparentconductive film. For example, JP 2001-35262 A proposes a thin film madeof a tin oxide in which the absorption coefficient is suppressed to below within such a wavelength range that a solar cell can utilizeeffectively.

In the above-noted thermal decomposition methods, however, the formationof the thin film virtually denotes crystal growth in the case where themetal oxide is crystalline; therefore, the conditions of the crystalgrowth in the thin film change considerably depending on the conditionsof the surface of the substrate or the like on which the thin film isformed. Specifically, if what serves as starting points for crystalgrowth exists in large numbers on the surface of a substrate on whichthe thin film is formed, crystal growth starts from numerous points, andconsequently, the crystal growth, that is, the thickness of the thinfilm, becomes relatively uniform. On the other hand, if what serves asstarting points for the crystal growth exists in fewer numbers on thatsurface, each one of the crystals grows large before the formation ofcrystal nuclei in the case of a raw material with faster reactivitybeing used, and a variation in film thickness therefore becomes large.Moreover, crystals become more difficult to grow, slowing down the filmdeposition rate. In turn, if the formation temperature of the thin filmis increased to complement the slowing down of the film deposition rate,the variation in film thickness becomes even larger.

For example, an example in JP 2(1990)-175631 A describes that a tinoxide thin film is formed at a glass temperature of 580° C. using tintetrachloride. When a tin oxide thin film is formed under thiscondition, no problem arises in terms of the performance of the thinfilm except that the film deposition rate is slow; however, a furtherexperiment performed by the present inventors proved that when the thinfilm was formed with the glass temperature elevated to 615° C., theglass surface was observed to have a white turbidity. When the portionwith the white turbid condition was observed with an electronmicroscope, giant crystal grains that were as large as 2 μm in diameterwas observed, together with the adjacent portions in which crystalgrains are absent. This seems to be because, before crystal nuclei wereformed uniformly on the glass surface, initially-formed nuclei had grownabruptly, forming a large unevenness on the glass surface, and thus,when macroscopically seen, the haze ratio (haze factor) considerablyincreased.

Further, Example 25 in JP 9(1997)-40442 A describes that, with amanufacturing process for a glass sheet using a float process, anundercoating film made of silicon oxide was deposited on a glass ribbonusing a CVD method, and subsequently a thin film made of tin oxide wasformed at a film deposition rate of 6234 nm/min. However, since anundercoating film made of silicon oxide has a very smooth surface, it isobvious that when a thin film made of tin oxide is deposited at a filmdeposition rate of as fast as 6234 nm/min. without performing anytreatment thereto, giant crystal grains should form, causing a whiteturbidity. In this regard, JP 9(1997)-40442 A contains no descriptionconcerning the surface condition of the glass substrate of Example 25.

On the other hand, in JP 2862174 B, in which its object is to furthergrow crystal grains of tin oxide using tin chloride as a raw materialand to increase the film deposition rate to improve productivity, atransparent conductive film with a thickness of 350 nm or greater isdeposited by a thermal decomposition method on a surface of a glasssubstrate the temperature of which is higher than 615° C. When a filmdeposition is carried out at such a high temperature, crystal grains arenot uniformly formed in the surface, resulting in a white, turbidtransparent conductive film with a very high haze ratio. There has beena problem that if a photoelectric conversion device is constructed by anamorphous silicon layer formed on this transparent conductive film, theamorphous silicon film, which serves as the photoelectric conversionlayer, is not uniformly formed, and the efficiency of the solar cell isreduced.

Furthermore, there has been a problem when dimethyltin dichloride ormonobutyltin trichloride is used as tin materials other than thosedescribed above, in that although the white turbidity does not occur,the absorptance becomes large in the wavelength range of 400 to 700 nm,in which the light quantity of solar light spectrum reaching the Earth'sground is large, particularly in the short wavelength range thereof, andas a result, the incident light volume on the photoelectric conversionlayer in the solar cell is small. For example, JP 2001-35262 A describesabsorption coefficients of the tin oxide films using dimethyltindichloride or monobutyltin trichloride as a raw material; the absorptioncoefficient thereof is lowest at a wavelength of about 600 to 700 nm,and the absorption coefficient at 400 nm is 1.8 times or greater thanthat of the foregoing range.

DISCLOSURE OF THE INVENTION

This invention has been accomplished taking the foregoing problems intoconsideration. An object thereof is to provide a thin film-formingmethod by which, when a thin film containing a crystalline metal oxideas the main component is formed utilizing a thermal decomposition methodwithin a short time over a wide area, the thickness of the thin filmbecomes relatively uniform. Another object thereof is to prevent a whiteturbidity in a substrate provided with the thin film containing acrystalline metal oxide as the main component, as well as to prevent theformation of defect points in a functional film that is to be formed onthe thin film. A still further object is to provide a substrate providedwith a transparent conductive film that comprises a bump and depressionconfiguration that exhibits a light trapping effect effectively and thatshows less absorption of a short wavelength range of visible light, whenthis thin film containing a crystalline metal oxide as the maincomponent is used as a transparent conductive film for a photoelectricconversion device or the like, in order to increase the incident lightvolume to the photoelectric conversion layer. Yet another object thereofis to provide a photoelectric conversion device using the substrate.

In order to accomplish the foregoing objects, a thin-film forming methodaccording to this invention is characterized by forming, after disposingmetal-containing particles on a substrate, forming a thin filmcontaining a crystalline metal oxide as a main component by a thermaldecomposition method using a chloride of a metal as a raw material.

Alternatively, the method is for forming on a substrate a thin filmcontaining a crystalline metal oxide as the main component by a thermaldecomposition method using a chloride of a metal as a raw material,characterized in that the film deposition rate for a metal-containingthin film is slower than the film deposition rate for the thin filmcontaining a crystalline metal oxide as the main component, and the thinfilm containing the metal oxide as main component is directly depositedon the metal-containing thin film. The use of these thin film-formingmethods makes it possible, even when the thin film containing acrystalline metal oxide as the main component is formed at a high filmdeposition rate by a thermal decomposition method using a chloride of ametal as a raw material, to suppress the generation of giant crystalgrains of the metal oxide.

In another aspect, a substrate according to this invention comprises abuffer layer having a film thickness of 250 nm or less and a transparentconductive film deposited in that order by a thermal decompositionmethod using a tin chloride as a raw material. This substrate has thetransparent conductive film provided with relatively large and uniformsurface roughness and therefore is capable of scattering transmittedlight and reflected light efficiently at the surface. Therefore, whenthis substrate is used for a photoelectric conversion device, theconversion efficiency of the photoelectric conversion device can beincreased without causing defect points such as pinholes in thephotoelectric conversion layer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic view of an apparatus used for an online CVDmethod.

FIG. 2 is a photograph, image-processed into a black-and-white binaryimage, of a 90 nm-thick buffer layer photographed at a dip of 30° usinga scanning electron microscope (SEM).

FIG. 3 is a photograph, image-processed into a black-and-white binaryimage, of a 140 nm-thick buffer layer photographed at a dip of 30° usinga SEM.

FIG. 4 is a photograph, image-processed into a black-and-white binaryimage, of a 190 nm-thick buffer layer photographed at a dip of 30° usinga SEM.

FIG. 5 is a cross-sectional view of one example of a photoelectricconversion device to which the present invention is applied.

PREFERRED EMBODIMENTS OF THE INVENTION

Hereinbelow, preferred embodiments of this invention are described indetail. It should be noted that the invention is not intended to belimited by the following preferred embodiments.

A thin film-forming method according to this invention is a method offorming a thin film containing a crystalline metal oxide as a maincomponent on a substrate, using a thermal decomposition method,including: forming the thin film using a raw material containing achloride of a metal; and prior to the forming of the thin film, 1)disposing metal-containing particles on the substrate, or 2) forming, ata film deposition rate slower than a film deposition rate for the thinfilm, a metal-containing thin film on the substrate, wherein, in thecase of the step 2), the thin film containing the metal oxide as maincomponent is directly formed on the metal-containing thin film.

Herein, the term “metal-containing particle” is intended to mean a bodythat contains a metal, such as silicon, zinc, zirconium, indium, tin, ortitanium, the particle diameter of which is in a range of nanometers tosubmicrons. The metal-containing particle may be any of nitride, oxide,oxynitride, and complex, and the configuration thereof is notparticularly limited. The term “metal-containing thin film” denotes athin film that is deposited by a thermal decomposition method using achloride of a metal as a raw material and in which a metal exists as itsfilm substance. The metal existing as the film substance may be theabove-mentioned metal-containing particle or may be what is encompassedas a compositional component of the thin film. The term “thin filmcontaining a crystalline metal oxide as the main component” denotes,literally, those which have a crystalline metal oxide such as tin oxide,titanium oxide, zinc oxide, tin indium oxide doped with tin (ITO), andcadmium oxides as the main component.

Herein, the term “main component” denotes, according to convention, acomponent whose content is 50 mass % or greater among the compositionalcomponents. The characteristics of a thin film are mostly determined byits main component, and therefore, it will be appropriate to assess thecharacteristics of the thin film with the main component. Also, the term“transparent conductive film” denotes a thin film that is encompassed bythe thin film containing a crystalline metal oxide as the maincomponent, which has a crystalline metal oxide, such as tin oxide, zincoxide, ITO, and cadmium oxide, as the main component and has both alight-transmissive property and a conductive property.

The present inventors have conducted intensive studies focusing on thefact that the condition of crystal growth in a thin film containing acrystalline metal oxide as the main component changes depending on thesurface conditions of the substrate, and as a result have found thatcrystal growth of a metal oxide in the thin film containing acrystalline metal oxide as the main component can be made relativelyuniform by allowing a substance that can be starting points for crystalgrowth to be present on the substrate in advance of forming the thinfilm containing a crystalline metal oxide as the main component. Thesubstance that can be starting points for crystal growth is themetal-containing particle or metal-containing thin film, which have beenmentioned above.

Because of the presence of these, the starting points for crystal growthof metal oxide increase greatly in number and the crystal growth startsalmost simultaneously from numerous positions; therefore, the generationof giant crystal grains is suppressed in the formation of the thin film,and as a result, the thickness of the thin film becomes relativelyuniform. Thus, the metal-containing particles or metal-containing thinfilm disposed on a substrate serves the function of suppressing thegeneration of giant crystal grains in the formation of the thin film,and for this reason, these may also be collectively referred to as“buffer layer” hereinafter.

Generally, with a thin film containing a crystalline metal oxide as themain component, as the temperature of its formation becomes higher, thecrystal growth rate, i.e., the film deposition rate becomes faster;accordingly, from the viewpoint of industrial production efficiency,higher temperatures of formation are more preferable. This, however,causes the thickness to be considerably non-uniform, leading to problemsin appearance such as the white turbidity in the case of the substratebeing transparent, or problems in terms of performance such as thegeneration of particle-like defect points, which are called pinholes, inthe case of forming a functional film thereon. On the other hand,reducing the formation temperature of the thin film containing acrystalline metal oxide as the main component has an advantage in thatthe film thickness becomes relatively uniform, although the filmdeposition rate becomes slower. Accordingly, it will be appreciated thatif one can find a way to combine the advantage in the case of highformation temperatures and the advantage in the case of low formationtemperatures, it is possible to make the film thickness of a thin filmcontaining a crystalline metal oxide as the main component relativelyuniform while keeping the film deposition rate high. The presentinventors have made intensive studies on this and as a result havereached this invention. This invention makes it possible to suppress thegeneration of the pinholes and effectively prevent the area with awhite, turbid condition from expanding in cases where the filmdeposition rate for a thin film containing a crystalline metal oxide asthe main component is fast, particularly in cases where the temperatureof the reaction system is high.

The metal-containing particles exist on the substrate, forming bumps andfunctioning as starting points for crystal growth. The metal-containingthin film functions as starting points for crystal growth because it hasbumps originating from the particles on the thin film surface in caseswhere it contains the metal-containing particles, and because the metalcontained as a constituent component of the thin film attractscrystalline metal oxide and promotes crystal growth in cases where itdoes not contain the particles.

Regarding the metal-containing particles, it is preferable that theiraverage particle diameter be 5 to 500 nm in order that they function asnuclei for crystal growth and at the same time suppress the formation ofgiant crystal grains in the formation of the thin film containing acrystalline metal oxide as the main component. The method for providingthe metal-containing particles on a substrate is not particularlylimited, but a preferable method is such that they are fixed to asubstrate heated at a high temperature by a powder spraying method, inorder that they can be disposed uniformly over the substrate and not beoverlaid on one another. It is desirable that the metal-containingparticles form a single layer and have a closest packed structure on thesubstrate; however, since they meet the purpose as long as they functionas the nuclei for crystal growth, there may be slight gaps between theparticles. When the gap between the particles is 100 μm or less, theparticles can contribute to uniformity in the thin film containing acrystalline metal oxide as the main component.

The metal of the metal-containing particles or the metal of themetal-containing thin film may be different from the metal of the thinfilm containing a crystalline metal oxide as the main component, but itis preferable that they are the same type of metal. When they are thesame type of metal, crystal growth is induced more in the thin film, andtherefore, the metal-containing particles can be made small in theparticle diameter thereof or fewer in number, or the content of themetal can be reduced in the metal-containing thin film. For example,when a thin film composed of tin oxide or titanium oxide that has arutile structure is formed as the metal-containing thin film, it isdesirable to deposit a film composed of tin oxide or titanium oxide withthe same rutile structure, or a film composed of titanium oxide with ananatase structure, which is similar to the rutile structure, as the thinfilm containing a crystalline metal oxide as the main component.

The buffer layer may be formed directly on the substrate, oralternatively, an undercoating film may be formed on the substrate andthe buffer layer may be formed thereon. The undercoating film isprovided for, for example when the substrate is glass, preventing analkaline component contained in the glass from thermally diffusing inthe buffer layer or the thin film containing a crystalline metal oxideas the main component. The undercoating film may be a closely-packedthin film containing silicon oxide, aluminum oxide, silicon oxynitride,silicon oxycarbide, or the like as the main component, or when theadhesive force between the substrate and the buffer layer is low, thefilm may be such that it contains both of the components of thesubstrate and the buffer layer to increase the adhesive force by meansof their affinity. Because of the presence of the undercoating film, thebuffer layer or the thin film containing a crystalline metal oxide asthe main component can be adhered to the substrate with sufficientstrength, and its characteristics do not easily degrade.

Further, the undercoating film may either be a single layer or becomposed of two layers. For example, the formation of an undercoatingfilm comprising a first undercoating layer (substrate side) having arefractive index of 1.6 to 2.5 and a thickness of 5 to 100 nm and asecond undercoating layer (buffer layer side) having a refractive index1.4 to 2.0 and a film of 5 to 100 nm between the substrate and thebuffer layer can reduce the reflectivity therebetween. Accordingly, byutilizing a light-transmissive conductive substrate that is providedwith this undercoating film for a photoelectric conversion device, theamount of light incident on the photoelectric conversion layer can beincreased. In addition to serving to reduce reflectivity and reflectedinterference colors, this undercoating film also serves, in cases wherethe substrate is a glass sheet containing an alkaline component, toprevent the alkaline component from diffusing into the buffer layer andthe thin film containing a crystalline metal oxide as the main componentand reducing their conductivity.

The first undercoating layer, which is in contact with the substrate,preferably should have as its main component at least one kind selectedfrom the group consisting of tin oxide, titanium oxide, zinc oxide, andaluminum oxide. The second undercoating layer, which is in contact withthe buffer layer, preferably should have as its main component at leastone kind selected from the group consisting of silicon oxide, aluminumoxide, silicon oxynitride, silicon oxycarbide, and tin oxide. If theundercoating film is too thin, the above-described function ofpreventing the alkaline component from diffusing cannot be exhibitedsufficiently. On the other hand, if it is too thick, the effect ofreducing reflectivity is lost, and the transmissivity also reduces.

In addition, in cases where the first undercoating layer is acrystalline thin film containing tin oxide or titanium oxide as the maincomponent, the surface roughness originated from crystal growth can bemade larger by increasing the thickness thereof. The surface roughnessof the first undercoating layer reflects the surface of the secondundercoating layer; therefore, when the first undercoating layer is madefairly thick, 40 to 100 nm, and at the same time the closely-packed,non-crystalline second undercoating layer is made fairly thin, 5 to 50nm, it is possible to make the surface roughness of the undercoatingfilm greater and to further prevent the alkaline component contained inthe glass sheet from diffusing into the buffer layer and the thin filmcontaining a crystalline metal oxide as the main component in a reliablemanner.

Further, in cases where the substrate is a glass sheet containing analkaline component, by using a raw material containing a halogen, bumpsor depressions that are larger than the surface roughness originatedfrom crystal growth can be formed on the surface first undercoatinglayer in the formation of the first undercoating layer by a thermaldecomposition method. Regarding such relatively large bumps ordepressions, the alkaline component in the glass sheet and the halogencontained in the raw material for the first undercoating layer reactwith each other, forming alkali-halogen particles, which are taken intothe first undercoating layer, forming bumps, or disappear therefrom dueto heat, forming depressions. These bumps and depressions are reflectedin the surface shape of the second undercoating layer. Accordingly, ifthe first undercoating layer that is crystalline and the secondundercoating layer that is non-crystalline are formed by a thermaldecomposition method, it is possible to reflect the surface roughnessoriginating from the crystal growth and the above-noted bumps ordepressions in the surface shape of the undercoating film. This istantamount to being capable of processing the surface of theundercoating film to be in a non-flat state, and for this reason, if theabove-described undercoating film is formed by a thermal decompositionmethod, the film deposition rate for the buffer layer can be quickened,as described above.

It should be noted that the phrase “the surface of the undercoating filmis non-flat” denotes a state that is clearly distinguished from the casein which a non-crystalline undercoating film is formed directly on aglass sheet, and specifically, it means that the surface of theundercoating film has a level difference of 1 nm or larger.

On the other hand, even if the substrate was glass, the undercoatingfilm is not necessarily required when the substrate is aluminosilicateglass, borosilicate glass, quartz glass, or the like, which does notcontain alkaline components. Nevertheless, there are cases in which theundercoating film is necessary for other purposes than preventing analkaline component from diffusing, as described above, and it should notbe interpreted as excluding the provision of the undercoating film on aglass that does not contain alkaline components.

Those glasses that do not contain alkaline components have higherthermal characteristics, such as glass transition temperature, than asoda lime glass, which contains an alkaline component, and therefore arecapable of forming a thin film containing a crystalline metal oxide asthe main component at higher temperatures. Moreover, glass isnon-crystalline and therefore the surface thereof is flat and smooth;likewise, the undercoating film that has silicon oxide as the maincomponent is also non-crystalline and therefore the surface is flat andsmooth. Since there exist no bumps that serve as starting points forcrystal growth on such a flat and smooth surface, it is necessary toprovide starting points for crystal growth by disposing themetal-containing particles or forming the metal-containing thin filmthereon. Accordingly, this invention exhibits its advantageous effectsparticularly effectively in the case of forming the thin film containinga crystalline metal oxide as the main component on a glass substratethat does not contain alkaline components or on the non-crystallineundercoating film thereabove.

The method for forming the metal-containing thin film is notparticularly limited as long as it is a thermal decomposition method,and examples include a CVD method and a solution-spraying method inwhich a solution material is sprayed onto a heated substrate. If themetal-containing thin film and the thin film containing a crystallinemetal oxide as the main component are formed by the same formationmethod, they can be formed within a short time through a series ofmanufacturing steps; for this reason, it is preferable that these beformed by the same method in terms of industrial production efficiency.

Because the metal-containing thin film needs to function as startingpoints for crystal growth in the thin film containing a crystallinemetal oxide as the main component, it is necessary that the film beformed uniformly on the surface of the substrate or of the undercoatingfilm, desirably with bumps at constant intervals on the surface. Forthat reason, the film deposition rate for the metal-containing thin filmis slower than the film deposition rate for the thin film containing acrystalline metal oxide as the main component. Specifically, the filmdeposition rate should preferably be 20 to 2500 nm/min. Nevertheless, inthe case of the film deposition rate exceeding 600 nm/min., it ispreferable that the surface of the undercoating film (secondundercoating layer) be provided with bumps and depressions. Even if thefilm deposition rate for the metal-containing thin film itself is slow,the thickness thereof is 250 nm or less, as will be described later, andsignificantly thinner than that of the thin film containing acrystalline metal oxide as the main component (transparent conductivefilm); therefore, the film deposition rate as a whole, which includesthat for the thin film containing a crystalline metal oxide as the maincomponent, is not degraded considerably. Rather, because of the presenceof the metal-containing thin film, the film deposition rate for the thinfilm containing a crystalline metal oxide as the main component can bemade faster; therefore, if the metal-containing thin film is formed tobe relatively thin and in addition the thin film containing acrystalline metal oxide as the main component is formed more quickly ata higher temperature, the film deposition rate as a whole can be madefaster.

Examples of the means to make the film deposition rate for themetal-containing thin film slower than the film deposition rate for thethin film containing a crystalline metal oxide as the main componentinclude a means in which the surface temperature of the substrate or theundercoating film is set to be fairly low in forming themetal-containing thin film and thereafter, after reheating, the thinfilm containing a crystalline metal oxide as the main component isformed, and a means in which a raw material with low reactivity is used.Nevertheless, in cases where, the undercoating film, themetal-containing thin film, and the thin film containing a crystallinemetal oxide as the main component are formed successively on a glassribbon in a float process by a CVD method, the temperature of reactionsystem during the formation of the metal-containing thin film formbecomes higher than the temperature of reaction system during thedeposition of the thin film containing a crystalline metal oxide as themain component. In this case, it is conceivable to reheat the glassribbon using a burner or the like after the formation of themetal-containing thin film in order to make the temperature of reactionsystem for the thin film containing a crystalline metal oxide as themain component higher, but by doing so, temperature unevenness may occurin the glass ribbon, leading to the risk of degrading the formability ofglass. In view of this case, it is desirable to reduce reactivity byvarying the types of raw materials, or to lower the film deposition rateby reducing the thickness of the metal-containing thin film. For thechloride of a metal, those which do not contain organic substances, suchas tin dichloride, tin tetrachloride, titanium chloride, zinc chloride,and indium chloride, are suitable for the purpose of reducing theenvironmental load.

The metal-containing thin films may be those including metal-containingparticles, or those that contain a metal as its compositional component.For example, when a metal-containing thin film that has a crystallinemetal oxide such as tin oxide or titanium oxide as the main component isformed by a CVD method, bumps that can be clearly distinguished from theother portion may be formed on the thin film in some cases, but in othercases, very small bumps and depressions are formed on the surface andthe vertices of those bumps and depressions need to be interpreted asthe bumps. In other words, a surface shape of a metal-containing thinfilm may not be determined easily if it is part of surface roughness orcan be considered as a bump. In this invention, it is sufficient thatthe metal-containing thin film functions as starting points for crystalgrowth, and even if it cannot be distinguished clearly whether a shapeforms a vertex of the surface roughness or a bump, that is not a problemper se as long as the foregoing function is fulfilled. Additionally,even if the metal-containing thin film does not haveclearly-distinguishable bumps formed on the surface thereof, thefunction as the starting points for crystal growth can be fulfilled whencrystal growth can be induced in the thin film containing a crystallinemetal oxide as the main component.

For reference, it has been confirmed that in the case of forming themetal-containing thin film by a CVD method, white turbidity is notproduced in the thin film containing a crystalline metal oxide as themain component even with increased film deposition rates for themetal-containing thin film and increased film thicknesses when theconcentration of a metal-containing gas in the mixed gas, which servesas the raw material therefor, is lowered. This seems to be because thelowering of the concentration of the metal-containing gas suppressesabrupt crystal growth that originates from the high concentrationmetal-containing gas residing locally.

The metal-containing thin film should preferably be in a condition suchthat the thickness is 10 to 250 nm, and the surface thereof has amultiplicity of bumps formed thereon and having a height of 10 to 200nm. When the thickness is less than 10 nm, there is a risk of theundercoating film being not completely covered; on the other hand, whenexceeding 250 nm, the bumps become too large and too high, the risk ofgenerating giant crystal grains in the thin film containing acrystalline metal oxide as the main component increases. The morepreferable thickness of the metal-containing thin film is 30 to 200 nm.

After forming the buffer layer with the above-mentioned means, the thinfilm containing a crystalline metal oxide as the main component isformed using a thermal decomposition method. Due to the presence of thebuffer layer, the thin film containing a crystalline metal oxide as themain component does not easily cause variations in film thicknessbecause the crystal growth starts to take place from numerous startingpoints. Therefore, the thin film-forming method according to thisinvention makes it possible to form a defect-free, high quality thinfilm containing a crystalline metal oxide as the main component withincreased production efficiency because giant crystal grains are notgenerated even when the film deposition rate for the thin filmcontaining a crystalline metal oxide as the main component is madefaster.

The chloride of a metal that is a raw material for the thin filmcontaining a crystalline metal oxide as the main component shouldpreferably be in a gaseous state in the vicinity of the substrate.Accordingly, it may be in a liquid state on the way in which it issupplied to the vicinity of the substrate. That is, although a CVDmethod, in which the medium containing the chloride of a metal issupplied in a gaseous state, is desirable, it is also possible to employa solution-spraying method, in which it is liquid on the way, or apowder spraying method, in which it is in a solid state. In a CVDmethod, it is preferable that the respective raw materials be separatelysupplied through separate lines so that the chloride of a metal in agaseous state reacts with an oxidizing material or the like in thevicinity of the substrate. On the other hand, in cases where the rawmaterials are pre-mixed halfway on the supply line, a white turbid,high-haze condition tends to occur in a wide area of the thin filmcontaining a crystalline metal oxide as the main component at lowformation temperatures. This is because, with the pre-mixing, the rawmaterials in a gaseous state bring about a reaction before they reachthe vicinity of the substrate, making them more liable to generate giantcrystal grains in cases where there are fewer starting points forcrystal growth on the substrate. Therefore, this invention exhibits itsadvantageous effects more effectively in the case of pre-mixing the rawmaterials.

Although the method for forming the thin film containing a crystallinemetal oxide as the main component is not particularly limited as long asit is a thermal decomposition method, a method in which the arranging ofthe metal-containing particles or the formation of the metal-containingthin film can be performed in a serious of steps is preferable. Anexample is a method in which the metal-containing thin film is formedusing a CVD method and thereafter the thin film containing a crystallinemetal oxide as the main component is formed successively. In this case,however, since the formation temperature for the thin film containing acrystalline metal oxide as the main component becomes lower than thatfor the formation of the metal-containing thin film form, it isdesirable to utilize a material with good reactivity, such astetrachloride, for the raw material of the thin film containing acrystalline metal oxide as the main component. Moreover, when watervapor is used as the main raw material for the oxidizing material andoxygen is eliminated, it becomes possible to promote decomposition ofthe chloride of a metal and increase the film deposition rate.

It should be noted that in cases where the thin film containing acrystalline metal oxide as the main component is formed over a pluralityof times, for example, in cases where, with a CVD method, the film isdeposited gradually using a plurality of coaters, the advantageouseffects of this invention can be exhibited if the film deposition ratewith the raw material supplied from any one of the coaters is fasterthan the film deposition rate for the metal-containing thin film.

The formation of the thin film containing a crystalline metal oxide asthe main component may be carried out by a method in which, in the casewhere the substrate is a glass sheet, molten glass is first formed andcut into a desirable size, and thereafter the cut pieces are heated at ahigh temperature of higher than 615° C. to form the film by a thermaldecomposition method. In addition, it is possible to adopt a method inwhich, in a glass sheet manufacturing process with a float process, theabove-mentioned various raw materials are applied onto the surface of aglass ribbon in a float bath to form the film by a thermal decompositionmethod utilizing the heat retained by the glass ribbon (hereafter, themethod is referred to as “online CVD method”). In the online CVD method,since the temperature of the glass ribbon is even higher, theadvantageous effects of this invention are exhibited more effectively.In an examination performed by the present inventors, it was confirmedthat when the thin film containing a crystalline metal oxide as the maincomponent is formed without the buffer layer, the area with the whiteturbid condition widens as the temperature of the substrate, such as thecut glass or the glass ribbon, increases. In other words, theadvantageous effects of the buffer layer becomes greater when thetemperature of the transparent substrate or the undercoating film ishigher.

When a buffer layer is formed on the substrate, the film deposition ratefor the thin film containing a crystalline metal oxide as the maincomponent can be increased to 2700 nm/min. or higher, or even to 3500nm/min. or higher. In particular, when the undercoating film, themetal-containing thin film, and the thin film containing a crystallinemetal oxide as the main component are formed in that order using theonline CVD method, the temperature of the reaction system in theformation of the thin film containing a crystalline metal oxide as themain component (the surface temperature of the glass ribbon immediatelytherebefore) can be elevated to 615° C. or higher, or even to a range of620° C. to 750° C. For example, when the above-noted surface temperatureis 650° C. or higher, the film deposition rate reaches as high as 6300to 20000 nm/min. Nevertheless, even when the thin film containing acrystalline metal oxide as the main component is formed at such fastfilm deposition rates, this glass substrate does not produce a whiteturbidity as long as the buffer layer is formed.

As raw materials for the metal-containing thin film and the thin filmcontaining a crystalline metal oxide as the main component that are usedin the thermal decomposition method, it is preferable to use chloridesof tin and titanium. Examples of tin materials include tintetrachloride, dimethyltin dichloride, dibutyltin dichloride,tetramethyltin, tetrabutyltin, dioctyltin dichloride, monobutyltintrichloride, and dibutyltin diacetate, and in particular, theabove-described advantageous effects are exhibited effectively when tintetrachloride is a raw material. Examples of the oxidizing material usedfor forming tin oxide from the tin materials include water vapor,oxygen, air, alcohols such as methyl alcohol and ethyl alcohol. Forreference, by using water vapor and oxygen in combination or byincreasing the concentration of water vapor, the absorption coefficientof the thin film containing a crystalline metal oxide as the maincomponent in the wavelength range of 600 to 800 nm can be reduced. Inthe case of using water vapor and oxygen in combination, theconcentration of water vapor should preferably be 30 to 70 mol/L and theconcentration of oxygen 5 to 30 mol/L, whereas in the case of using onlywater vapor, its suitable concentration is 40 to 95 mol/L. When atransparent conductive film containing tin oxide as the main componentis deposited as the thin film containing a crystalline metal oxide asthe main component, it is preferable to add a compound of antimony orfluorine thereto in order to improve its conductivity. Examples of thecompound of antimony include antimony trichloride and antimonypentachloride, and examples of the fluorine compound include hydrogenfluoride, trifluoroacetic acid, bromotrifluoromethane, andchlorodifluoromethane. In order to enhance the conductivity further,these should preferably be used in combination. A preferable fluorineconcentration in the transparent conductive film is 0.2 mass % or less.In this case, the refractive index of the transparent conductive film isabout 1.9.

In the case of forming the undercoating film by a thermal decompositionmethod, examples of raw materials for silicon oxide suitable as theundercoating film include monosilane, disilane, trisilane,monochlorosilane, dichlorosilane, 1,2-dimethylsilane,1,1,2-trimethyldisilane, 1,1,2,2-tetramethyldisilane, tetramethylorthosilicate, and tetraethyl orthosilicate. Examples of the oxidizingmaterials in this case include oxygen, water vapor, dry air, carbondioxide, carbon monoxide, nitrogen dioxide, and ozone. It should benoted that in the case of using silane, an unsaturated hydrocarbon gas,such as ethylene, acetylene, or toluene, may be used in combination forthe purpose of preventing the silane from reacting before reaching theglass surface. Likewise, examples of raw materials for aluminum oxidesuitable as the undercoating film include trimethylaluminum, aluminumtriisopropoxide, diethylaluminum chloride, aluminum acetylacetonate, andaluminum chloride. Examples of the oxidizing materials in this caseinclude oxygen, water vapor, and dry air.

Types and configurations of the substrate are not particularly limited.Those that have conventionally provided with a thin film containing acrystalline metal oxide as the main component may be used as they are.For example, when a thin film containing a crystalline metal oxide asthe main component is formed on a transparent substrate such as glass,the haze ratio of the glass substrate reduces because giant crystalgrains are not formed. Accordingly, glass products provided with thethin film containing a crystalline metal oxide as the main component canexhibit such functions originating from the thin film as theelectro-magnetic-wave-shielding function, the heat-ray-reflectingfunction, and the electrical conducting function effectively withoutcausing problems such as forming a white turbidity.

Hereinbelow, a preferred embodiment with an online CVD method isdescribed in more detail. As illustrated in FIG. 1, in an apparatus usedfor the online CVD method, a glass ribbon 10 flows out from a meltingfurnace (float furnace) 11 into a float bath 12 and moves on a tin bath15 in a belt-like form, and a predetermined number of coaters 16 (threecoaters 16 a, 16 b, and 16 c in the embodiment illustrated in thefigure) that are spaced apart from the surface of the glass ribbon 10are provided in the tin float bath. From these coaters, gaseous rawmaterials are supplied so that the undercoating film, themetal-containing thin film, and the thin film containing a crystallinemetal oxide as the main component are successively formed on the glassribbon 10. Although not shown in the figure, it is possible to adoptmore coaters so that the undercoating film may have a two-layeredconfiguration, or the thin film containing a crystalline metal oxide asthe main component may be deposited by supplying raw materials from aplurality of coaters. The glass ribbon 10 on which the thin filmcontaining a crystalline metal oxide as the main component is formed ispulled up by rollers 17 and is transferred to an annealing furnace 13.The glass ribbon that has been annealed in the annealing furnace 13 iscut into glass sheets having a predetermined size by a cutting device,which is not shown in the figure. For the formation of the thin filmcontaining a crystalline metal oxide as the main component, it ispossible to use a solution-spraying method, in which various rawmaterials are supplied in a liquid state onto the glass ribbon that hascome out of the float bath 12, or a powder spraying method, in which theraw materials are supplied in a solid state, in combination with the CVDmethod in the float bath.

With the online CVD method as well, it is desirable that raw materialsbe transferred through separate lines in the coaters so that they mix inthe vicinity of the glass ribbon, and this invention makes it possibleto use them in a pre-mixed form. Using pre-mixed raw materials causestheir reaction to start at an early stage in the coaters and thus tendsto form giant crystal grains in the thin film containing a crystallinemetal oxide as the main component. In fact, in conventional online CVDmethods, a white turbidity has been caused with the surface temperatureof the glass ribbon being at about 600° C. in the case of usingtetrachloride as a chloride of a metal, if the raw materials used arepre-mixed. By contrast, according to this invention, even when pre-mixraw materials are supplied onto a glass ribbon the surface temperatureof which is at 620 to 750° C., the glass does not cause a whiteturbidity. In addition, pre-mixing raw materials has many advantages interms of industrial manufacturing process, such as temperature controlsare made simple until they are supplied to the coaters.

Moreover, the present inventors found that, in the case of depositing atransparent conductive film containing tin oxide as the main componentby a thermal decomposition method using tin chloride as a raw material,the transparent conductive film can be prevented from causing ahigh-haze state effectively by making the thickness of the buffer layerbe 250 nm or less.

The thickness of the buffer layer should preferably be 10 nm or greaterso that it can cover the entire surface of the substrate. If thethickness is less than 10 nm, it is difficult to cover the entiresurface of the substrate. On the other hand, if it is too thick, thesurface roughness of the buffer layer become too large, adverselyaffecting uniformity in the transparent conductive film. Accordingly,the thickness of the buffer layer needs to be 250 nm or less, or shouldmore preferably be 150 nm or less.

For the transparent conductive film, it is desirable that the absorptioncoefficient thereof be 1×10³ cm⁻¹ or less in the wavelength range of 400to 700 nm, the maximum value of the absorption coefficient be 1.7 timesor less the minimum value, and the sheet resistance be 15 Ω/□ (square)or less, for use as a transparent conductive film for a solar cell. Thewavelength range of 400 to 700 nm is a region in which the lightquantity of the solar light spectrum that reaches the Earth's ground islarge and therefore is considered as an important wavelength range interms of increasing the photoelectric conversion efficiency in a solarcell. Reducing the absorption in the transparent conductive film withinthe entire wavelength range leads to an increase in the quantity oflight that enters the photoelectric conversion layer. Research by thepresent inventors proved that, when a thin film composed of tin oxidewas formed on a glass sheet using tin chloride at a high temperature,the absorption in the thin film composed of tin oxide was reduced in thewavelength range from 400 to 700 nm because unnecessary impuritycomponents were not added. Since the transparent conductive film alsoserves as an electrode in a solar cell and therefore, it is preferablethat the sheet resistance be lower; however, in conventional ones,reduction in the sheet resistance has led to an increase in theabsorption in the long wavelength range due to the absorption by freeelectrons and to an increase in the short wavelength range as well. Witha thin film-forming method according to this invention, in cases where atransparent conductive film containing tin oxide as the main componentis deposited on a substrate using tin chloride at high temperatures, theabsorption coefficient is 1×10³ cm⁻¹ or lower in the wavelength range of400 to 700 nm and the absorption coefficient can be reduced so that themaximum value is 1.7 times or less of the minimum value while the sheetresistance is kept at 15 Ω/□ or lower. Note that, although details ofthe method for measuring light absorption coefficients of transparentconductive films will be given in Examples, the light absorptioncoefficient for that including the buffer layer is taken as the lightabsorption coefficient of the transparent conductive film forconvenience in measurement.

In addition, by providing a surface roughness on the surface of thetransparent conductive film as described above, the light-trappingeffect is caused to occur, improving photoelectric conversion efficiencyof photoelectric conversion devices represented by solar cells. As ameans to provide a surface roughness, the thickness of the transparentconductive film conventionally has been increased. The transparentconductive film has tin oxide as the main component and accordingly iscrystalline, so when the thickness is larger, individual crystals arelarger and its surface roughness is greater. However, an increasedthickness of the transparent conductive film causes the problem ofabsorption as described above. Thus, the transparent conductive film isrequired to be thin, and moreover, to have relatively large and uniformsurface roughness. In order to deposit such a transparent conductivefilm, increasing the thickness of the buffer layer is effective. Whenthe thickness of the buffer layer is increased, the surface roughness ofthe buffer layer can be made larger, and the transparent conductive filmformed thereon is provided with the above-noted relatively large surfaceroughness as the starting points for crystal growth; therefore, it ispossible to make the transparent conductive film be made thin and at thesame time to make the surface roughness large. Nevertheless, when thesurface roughness of the buffer layer become larger than are necessary,various problems arise, such that a white turbidity appears in thetransparent conductive film as described above or that the filmdeposition rate as a whole, including that of the buffer layer, slowsdown even if the transparent conductive film can deposited at highspeed. For that reason, a larger thickness of the buffer layer is notnecessarily desirable, and a suitable range of the thickness isrestricted to a range in which the surface roughness of the transparentconductive film can be appropriately large. Specifically, the thicknessof the buffer layer needs to be 250 nm or less; it should preferably be100 to 200 nm, and most preferably be 140 to 150 nm.

In order to study the relationship between the thickness of the bufferlayer and its surface roughness, a first undercoating layer composed oftin oxide, a second undercoating layer composed of silicon oxide, and ametal-containing thin film (buffer layer) having tin oxide as the maincomponent are formed on a glass substrate in that order by a CVD method,with varied thicknesses of the buffer layer. For the samples thusobtained, the buffer layers were photographed at a dip of 30° with ascanning electron microscope (SEM). FIGS. 2 to 4 show the SEMphotographs, image-processed into a black-and-white binary image. FIG. 2shows the case of the buffer layer being 90 nm, FIG. 3 the case of thebuffer layer being 140 nm, and FIG. 4 the case of the buffer layer being190 nm; these have the same configuration except that the thickness ofthe buffer layer is varied. As clearly seen from the comparison betweenFIGS. 2 to 4, the thicker the buffer layer is, the larger the surfaceroughness is. The size of the surface roughness of the transparentconductive film formed on the buffer layer becomes larger approximatelyproportionately to the surface shape of the buffer layer.

The sheet resistance of the transparent conductive film, specifically,preferably should be 5 to 15 Ω/□. The sheet resistance is measured usingcommercially available equipment that makes use of a four-probe method.For that reason, slight influences from the buffer layer or theundercoating film appear on the sheet resistance values. Taking theforegoing range of the sheet resistance value into account, thepreferable film thickness of the transparent conductive film is from 500to 2000 nm. Nevertheless, taking absorption for visible light asdescribed above into account, the more preferable film thickness is 500to 1000 nm. As will be described later in Examples, the substrateaccording to this invention makes it possible to increase the haze ratioas high as 12% or higher even when the thickness of transparentconductive film is 1000 nm or less.

It should be noted that the transparent conductive film may contain atrace amount of other components such as silicon, aluminum, zinc,copper, indium, bismuth, gallium, boron, vanadium, manganese, andzirconium. Nevertheless, the concentration of these trace-amountcomponents should preferably be 0.02 mass % or less.

Hereinbelow, the description discusses a case in which a substrateprovided with the buffer layer and the transparent conductive film isutilized for a photoelectric conversion element. As illustrated in FIG.5, a photoelectric conversion element is obtained by forming, on asubstrate 30, undercoating films 31 and 32, a buffer layer 33, atransparent conductive film 34, photoelectric conversion layers 37 and38 of thin films composed of amorphous silicon or crystalline silicon orsimilar films, and a conductive film (back electrode) 35 successively. Adevice in which the photoelectric conversion element is incorporated andvarious components are associated and assembled into an unit so that,for example, as a solar cell, electric energy can be taken out fromlight energy, is referred to as a photoelectric conversion device.

The photoelectric conversion layer may be a single layer configuration,or may have a configuration in which a plurality of layers are stacked.It may be a thin film composed of conventional amorphous silicon, or maybe a thin film composed of crystalline silicon. Further, a thin film 37composed of amorphous silicon and a thin film 38 composed of crystallinesilicon are combined to form a so-called hybrid tandem type. In the caseof hybrid tandem type, generally, a thin film composed of amorphoussilicon is formed on the transparent conductive film, and a thin filmcomposed of crystalline silicon is formed thereover.

The thin film composed of amorphous silicon is formed by depositing p-,i-, and n-type semiconductor layers in that order by a plasma CVDmethod. Specifically, examples include a film in which the followinglayers are deposited in that order: a p-type microcrystallinesilicon-based layer doped with boron atoms, which areconductivity-determining impurity atoms, at 0.01 atom % or more; anintrinsic non-crystalline silicon layer, which primarily serves forphotoelectric conversion; and an n-type microcrystalline silicon-basedlayer doped with phosphorus atoms, which are conductivity-determiningimpurity atoms, at 0.01% or more. Nevertheless, these respective layersare not limited to the foregoing, and for example, it is possible to usea non-crystalline silicon-based layer for the p-type layer, or to usealuminum as the impurity atoms in the p-type microcrystallinesilicon-based layer. Further, alloy materials of non-crystalline ormicrocrystalline silicon carbide or silicon germanium may be used as thep-type layer. The film thickness of the conductive-type (p-type, n-type)microcrystalline silicon-based layer should preferably be 3 to 100 nm,or more preferably 5 to 50 nm. The film thickness of the intrinsicnon-crystalline silicon layer should preferably be 0.05 to 0.5 μm. In aphotoelectric conversion element provided with an amorphous silicon thinfilm, however, it is possible to employ a non-crystalline siliconcarbide layer (e.g., a non-crystalline silicon carbide layer composed ofnon-crystalline silicon containing 10 atom % or less of carbon) or anon-crystalline silicon germanium layer (e.g., a non-crystalline silicongermanium layer composed of non-crystalline silicon containing 30 atom %or less of germanium), which are alloy materials, in place of theintrinsic non-crystalline silicon layer. It is preferable that theintrinsic non-crystalline silicon layer be deposited at a substratetemperature of 450° C. or lower in a plasma CVD method. This layer isformed to be a thin film that is substantially intrinsic semiconductive,the density of the conductivity-type-determining impurity atoms of whichis 1×10¹⁸ cm⁻³ or less.

The thin film composed of crystalline silicon can be formed bydepositing p-, i-, and n-type semiconductor layers in that order by aplasma CVD method in a similar procedure to that for the foregoing thinfilm composed of amorphous silicon. Alternatively, it can be formed byelectron beam vapor deposition using silicon as a raw material, a plasmaCVD method that utilizes glow discharge and uses monosilane diluted witha hydrogen gas as a raw material, or a thermal CVD method usingmonosilane or dichlorosilane. It is preferable that the film thicknessof the thin film composed of crystalline silicon be 0.1 to 10 μm, andparticularly preferably 5 μm or less. This thin film is formed at, forexample, a low temperature of 450° C. or lower in the plasma CVD methodand therefore contains a relatively large number of hydrogen atoms forterminating or inactivating grain boundaries and defects in the grains.The hydrogen content in the layer is preferably in a range of 0.5 to 30atom %, and particularly preferably in a range of 1 to 20 atom %.

In the case of a hybrid tandem-type photoelectric conversion element,the thickness of thin film composed of amorphous silicon is preferably0.05 to 0.4 μm, and the thickness of the thin film composed ofcrystalline silicon is preferably 0.5 to 5 μm, although they may dependon the configuration of the photoelectric conversion device.

For reference, the spectral sensitivity characteristic of the thin filmcomposed of amorphous silicon becomes greatest in a wavelength range ofabout 500 to 600 nm, and it shows the sensitivity only in a wavelengthrange up to about 800 nm due to the optical energy gap. On the otherhand, the thin film composed of crystalline silicon shows thesensitivity up to about 1100 nm.

For the back electrode, it is preferable to form at least one layer of ametallic layer composed of at least one material selected from aluminum(Al), silver (Ag), gold (Au), copper (Cu), platinum (Pt), and chromium(Cr) by a sputtering method or a vapor deposition method. Further, it ispossible to form a layer composed of conductive oxide such as ITO, tinoxide, or zinc oxide between the photoelectric conversion layer and theback electrode.

The photoelectric conversion element provided with the thin filmcomposed of crystalline silicon generates a lower open-end voltage and ahigher short circuit current density than that provided with the thinfilm composed of amorphous silicon. For that reason, in a photoelectricconversion device provided with the thin film composed of crystallinesilicon, the transmissivity of the transparent conductive film has moreinfluence on its photoelectric conversion efficiency than the sheetresistance value thereof.

EXAMPLES

Hereinbelow, this invention is described in detail with reference toexamples. It should be understood, however, that the invention is notintended to be limited by the following examples.

Example 1

A 4-mm thick soda lime glass sheet that was cut into a size of 150×150mm was placed on a mesh belt and was passed through a heating furnace tobe heated to about 600° C. While transferring the heated glass sheetfurther, a mixed gas composed of monosilane, oxygen, and nitrogen wassupplied from a coater installed above the transfer line to form a thinfilm (undercoating film) having a film thickness of 25 nm and composedof silicon oxide on the glass sheet. After annealing the glass sheet,the glass sheet was again placed on the mesh belt and passed through theheating furnace to be heated to about 620° C. While transferring theheated glass sheet further, a mixed gas composed of tin tetrachloride(vapor), oxygen, water vapor, and nitrogen was supplied from a coaterinstalled above the transfer line to form a thin film (metal-containingthin film) having a film thickness of 30 nm and composed of tin oxide(SnO₂) on the undercoating film at a film deposition rate of 50 nm/min.This glass sheet was annealed and thereafter passed through a heatingfurnace again with it placed on the mesh belt, to be heated to about620° C. While transferring the heated glass sheet further, a mixed gascomposed of tin tetrachloride (vapor), water vapor, nitrogen, andhydrogen fluoride was supplied from a coater installed above thetransfer line to deposit a transparent conductive film composed offluorine-containing tin oxide (SnO₂:F) and having a film thickness of800 nm on the metal-containing thin film at a film deposition rate of670 nm/min. The gap between the coater and the glass sheet was set at 10mm, and a nitrogen gas was supplied beside the exhaust section in acurtain-like fashion so that the outside air did not intrude inside thecoaters during the formation of the transparent conductive film.

The glass sheet thus obtained had a haze ratio of 22% but showed nowhite turbidity. For measuring haze ratio, an integrating sphere wasused.

Example 2

A transparent conductive film was deposited in a similar manner toExample 1 except that the following points were changed, and the glasssheet was evaluated. The thickness of the undercoating film was changedto 20 nm; as for the metal-containing thin film, the thickness waschanged to 100 nm and the film deposition rate to 160 nm/min; and as forthe transparent conductive film, oxygen was added to the raw materials,the thickness was changed to 710 nm, and the film deposition rate waschanged to 470 nm/min.

This glass sheet had a haze ratio of 17% and showed no white turbidity.

Example 3

A transparent conductive film was deposited in a similar manner toExample 1 except that the following points were changed, and the glasssheet was evaluated. As the glass sheet, an aluminosilicate glass thatdoes not contain alkaline components was used; and as for themetal-containing thin film, using as a metal chloride titanium chloride(vapor) for the raw material, a thin film having a thickness of 20 nmand composed of titanium oxide was formed at a film deposition rate of30 nm/min. As for the transparent conductive film, oxygen and methylalcohol were added to the raw materials; the thickness was changed to900 nm and the film deposition rate was changed to 1000 nm/min.

This glass sheet had a haze ratio of 29% but showed no white turbidity.

Example 4

A transparent conductive film was deposited in a similar manner toExample 1 except that the following points were changed, and the glasssheet was evaluated. As for the metal-containing thin film, oxygenserving as an oxidizing material was eliminated, and it was formed to afilm thickness of 30 nm at a film deposition rate of 50 nm/min. As forthe transparent conductive film, oxygen was added to its raw materials,and it was deposited to a thickness of 400 nm at a film deposition rateof 330 nm/min.

This glass sheet had a haze ratio of 6% and showed no white turbidity.

Example 5

An undercoating film, a metal-containing thin film, and a transparentconductive film were formed on a glass ribbon in that order utilizing anonline CVD method. Specifically, 98 volume % of nitrogen and 2 volume %of hydrogen were supplied to the space inside a float bath so that theinside of the float bath is kept at a slightly higher pressure than thatoutside the bath. With the inside of the float bath being kept to be anon-oxidizing atmosphere, a mixed gas composed of dimethyltin dichloride(vapor), oxygen, nitrogen, and helium was supplied from a first coaterlocated on the most upstream side to form a thin film (firstundercoating layer) having a thickness of 35 nm and composed of tinoxide on the glass ribbon. Subsequently, a mixed gas composed ofmonosilane, ethylene, oxygen, and nitrogen was supplied from a secondcoater to form a thin film (second undercoating layer) having athickness of 25 nm and composed of silicon oxide on the firstundercoating layer. Further, a mixed gas composed of dimethyltindichloride (vapor), oxygen, water vapor, and nitrogen was supplied froma third coater to form a thin film (metal-containing thin film) having athickness of 100 nm and composed of tin oxide (SnO₂) on the secondundercoating layer having a surface temperature of 680° C. at a filmdeposition rate of 2500 nm/min. Using a coater installed on the furtherdownstream side, a mixed gas composed of tin tetrachloride (vapor),water vapor, nitrogen, helium, and hydrogen fluoride was supplied ontothe metal-containing thin film having a surface temperature of 630° C.to deposit a transparent conductive film having a film thickness of 670nm and composed of fluorine-containing tin oxide (SnO₂:F) at a filmdeposition rate of 16700 nm/min.

This glass sheet had a haze ratio of 17% and showed no white turbidity.

Example 6

A transparent conductive film was deposited in a similar manner toExample 5 except that the following points were changed, and the glasssheet was evaluated. The surface temperature of the metal-containingthin film was set at 660° C., and a transparent conductive film having afilm thickness of 380 nm was deposited at a film deposition rate of 9500nm/min.

This glass sheet had a haze ratio 6% and showed no white turbidity.

Example 7

As in Example 5, from the first coater, a mixed gas composed of tintetrachloride (vapor), water vapor, nitrogen, and helium was supplied toform a thin film (first undercoating layer) having a thickness of 45 nmand composed of tin oxide on a glass ribbon. In addition, from the thirdcoater, a mixed gas composed of tin tetrachloride (vapor), oxygen, watervapor, and nitrogen was supplied to form a thin film (metal-containingthin film) having a thickness of 90 nm and composed of tin oxide (SnO₂)on the second undercoating layer having a surface temperature of 680° C.at a film deposition rate of 1830 nm/min. Using a coater installed onthe further downstream side, a mixed gas composed of tin tetrachloride(vapor), water vapor, nitrogen, helium, and hydrogen fluoride wassupplied on the metal-containing thin film having a surface temperatureof 630° C. to deposit a transparent conductive film having a filmthickness of 691 nm and composed of fluorine-containing tin oxide(SnO₂:F) at a film deposition rate of 7030 nm/min. It should be notedthat the conditions that are not specified were similar to those inExample 5.

This glass sheet had a haze ratio of 20% and showed no white turbidity.

Example 8

An undercoating film, a metal-containing thin film, and a transparentconductive film were formed on a glass ribbon in that order utilizing anonline CVD method. Specifically, 98 volume % of nitrogen and 2 volume %of hydrogen were supplied to the space inside a float bath so that theinside of the float bath was kept at a slightly higher pressure thanthat outside the bath. With the inside of the float bath being kept tobe a non-oxidizing atmosphere, a mixed gas composed of monosilane,ethylene, oxygen, and nitrogen was supplied from a first coater locatedon the most upstream side to form on the glass a silicon oxide thin film(undercoating film) having a thickness of 25 nm. Further, a mixed gascomposed of tin tetrachloride (vapor), oxygen, water vapor, and nitrogenwas supplied from a second coater to form a thin film (metal-containingthin film) having a thickness of 25 nm and composed of tin oxide (SnO₂)on the undercoating film having a surface temperature of 680° C. at afilm deposition rate of 510 nm/min. Using a coater installed on thefurther downstream side, a mixed gas composed of tin tetrachloride(vapor), water vapor, nitrogen, helium, and hydrogen fluoride wassupplied onto the metal-containing thin film having a surfacetemperature of 630° C. to deposit a transparent conductive film having afilm thickness of 950 nm and composed of fluorine-containing tin oxide(SnO₂:F) at a film deposition rate of 5430 nm/min.

This glass sheet had a haze ratio of 18% and showed no white turbidity.

Example 9

An undercoating film, a metal-containing thin film, and a transparentconductive film were formed on a glass ribbon in that order utilizing anonline CVD method. Specifically, 98 volume % of nitrogen and 2 volume %of hydrogen were supplied to the space inside a float bath so that theinside of the float bath was kept at a slightly higher pressure thanthat outside the bath. With the inside of the float bath being kept tobe a non-oxidizing atmosphere, a mixed gas composed of tin tetrachloride(vapor), water vapor, nitrogen, and helium was supplied from a firstcoater located on the most upstream side to form a thin film (firstundercoating layer) having a thickness of 35 nm and composed of tinoxide on the glass ribbon. Subsequently, a mixed gas composed ofmonosilane, ethylene, oxygen, and nitrogen was supplied from a secondcoater to form a thin film (second undercoating layer) having athickness of 25 nm and composed of silicon oxide on the firstundercoating layer. Further, a mixed gas composed of tin tetrachloride(vapor), oxygen, water vapor, and nitrogen was supplied from a thirdcoater to form a thin film (metal-containing thin film) having athickness of 140 nm and composed of tin oxide (SnO₂) on the secondundercoating layer having a surface temperature of 680° C. at a filmdeposition rate of 2850 nm/min. Using a coater installed on the furtherdownstream side, a mixed gas composed of tin tetrachloride (vapor),water vapor, nitrogen, helium, and hydrogen fluoride was supplied ontothe metal-containing thin film having a surface temperature of 630° C.to deposit a transparent conductive film having a film thickness of 636nm and composed of fluorine-containing tin oxide (SnO₂:F) at a filmdeposition rate of 6470 nm/min.

This glass sheet had a haze ratio of 27% and showed no white turbidity.

Comparative Example 1

In a similar manner to Example 1, a thin film was layered on a glasssheet except that the metal-containing thin film was not formed and thetransparent conductive film was deposited directly on the undercoatingfilm.

This glass sheet was observed to have a white turbidity whose appearancewas like that seen in frosted glass.

Comparative Example 2

An undercoating film, a metal-containing thin film, and a transparentconductive film were formed on a glass sheet in a similar manner to thatin Example 1 except that the film deposition rate for themetal-containing thin film was changed to 900 nm/min.

This glass sheet showed a white turbidity considerably more than theglass of Comparative Example 1.

Comparative Example 3

A transparent conductive film was deposited by an online CVD method in asimilar manner to that in Example 5 except that the following pointswere changed, and the glass sheet was evaluated. The third coater wasstopped, and without forming the metal-containing thin film, atransparent conductive film having a film thickness of 600 nm wasdirectly deposited on the second undercoating layer at a film depositionrate of 15000 nm/min.

This glass sheet showed a white turbidity considerably more thanComparative Example 1. This seems to be because with the online CVDmethod, the transparent conductive film was deposited on the glassribbon at a high temperature, 630° C.

Comparative Example 4

A transparent conductive film was deposited in a similar manner toExample 5 by an online CVD method except that the following points werechanged, and the glass sheet was evaluated. A metal-containing thin filmhaving a thickness of 600 nm was formed on a second undercoating layerhaving a surface temperature of 690° C. at a film deposition rate of15000 nm/min. Further, on the metal-containing thin film having asurface temperature of 650° C., a transparent conductive film having afilm thickness of 300 nm was deposited at a film deposition rate of 7500nm/min.

This glass sheet showed a white turbidity.

Reference Example 1

A metal-containing thin film and a transparent conductive film wereformed on a glass sheet in a similar manner to that in Example 1 exceptthat no undercoating film was formed.

This glass sheet had a haze ratio of 35% and showed a slight whiteturbidity.

Next, with the substrates according to this invention, characteristicsrequired for a transparent conductive substrate in a photoelectricconversion device were examined.

Example 10

A 4-mm thick soda lime glass sheet that was cut into a size 150×150 mmwas placed on a mesh belt and passed through a heating furnace to beheated to about 600° C. While transferring the heated glass sheetfurther, a mixed gas composed of monosilane, oxygen, and nitrogen wassupplied from a coater installed above the transfer line to form a thinfilm (undercoating film) having a film thickness of 25 nm and composedof silicon oxide on the glass sheet. After annealing the glass sheet,the glass sheet again was placed on the mesh belt and passed through theheating furnace to be heated to about 620° C. While transferring theheated glass sheet further, a mixed gas composed of tin tetrachloride(vapor), oxygen, water vapor, nitrogen was supplied from a coaterinstalled above the transfer line to form a metal-containing thin filmhaving a film thickness of 30 nm and composed of tin oxide on theundercoating film at a film deposition rate of 50 nm/min. This glasssheet was annealed and thereafter passed through a heating furnace againwith it placed on the mesh belt to be heated to about 620° C. Whiletransferring the heated glass sheet further, a mixed gas composed of tintetrachloride (vapor), water vapor, nitrogen, and hydrogen fluoride wassupplied from a coater installed above the transfer line to deposit atransparent conductive film composed of fluorine-containing tin oxide(SnO₂:F) and having a film thickness of 800 nm on the metal-containingthin film at a film deposition rate of 670 nm/min. Also, the gap betweenthe coater and the glass sheet was set at 10 mm, and a nitrogen gas wassupplied beside the exhaust section in a curtain-like fashion so thatthe outside air did not intrude inside the coaters during the formationof the transparent conductive film.

The haze ratio of this glass sheet provided with the transparentconductive film, which was measured using an integrating sphere, was22%, and no white turbid, high-haze state was observed. Thereflectivity, absorption coefficient, and sheet resistance are shown inTable 1 below. The reflectivity was obtained by averaging the valueswith 10 nm intervals in a wavelength range of 400 to 1100 nm, measuredfrom the surface of the glass sheet on which the transparent conductivefilm is not provided. The absorption coefficients were obtained in thefollowing manner for wavelengths of 400, 500, 600, and 700 nm.

Measurement of Absorption Coefficient

Methylene iodide having a refractive index of 1.79 was applied on thetransparent conductive film deposited according to the foregoing Example10, and a cover glass having a thickness of 1 mm (#7059 manufactured byCorning Inc.) was brought into close contact from thereabove, to preparea sample in which scattering loss due to the surface roughness of thetransparent conductive film is eliminated. The transmissivity andreflectivity of this sample in the visible light range were measuredwith a spectrophotometer, and from the results, the absorption rate wasobtained. Meanwhile, methylene iodide was supplied onto a soda limeglass sheet provided with only the undercoating film according toExample 10, and the above-noted cover glass was brought into closecontact from thereabove to prepare a reference sample; with thisreference sample as well, the absorptance in the visible light range wasobtained in a similar manner to the above. The absorptance of thereference sample was subtracted from the absorptance of the sample, andfurther by solving the equation taking multiple reflection intoconsideration, the absorption coefficient of the transparent conductivefilm was obtained.

Example 11

A glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 10 except that the conditions werechanged as specified in the following. On the glass sheet, a thin film(undercoating film) having a film thickness of 20 nm and composed ofsilicon oxide was formed, and a metal-containing thin film having a filmthickness of 100 nm was formed thereon at a film deposition rate of 170nm/min. Further, a mixed gas composed of tin tetrachloride (vapor),oxygen, water vapor, nitrogen, and hydrogen fluoride was supplied todeposit a transparent conductive film having a thickness of 720 nm andcomposed of fluorine-containing tin oxide (SnO₂:F) on themetal-containing thin film at a film deposition rate of 480 nm/min.

This glass sheet had a haze ratio of 17% and did not show a whiteturbid, high-haze state. The reflectance, absorption coefficient, andsheet resistance thereof are collectively shown in Table 1 below.

Example 12

A glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 10 except that the conditions werechanged as specified in the following. A mixed gas composed of tintetrachloride (vapor), water vapor, and nitrogen was supplied to form ametal-containing thin film having a film thickness of 50 nm on theundercoating film at a film deposition rate of 510 nm/min. Theobservation of this buffer layer with an electron microscope confirmedthat tin oxide was in a granular state (a state in which individualcrystals are clearly larger than those in the metal-containing thin filmof Example 10) on the undercoating film. A mixed gas composed of tintetrachloride (vapor), oxygen, water vapor, nitrogen, and hydrogenfluoride was supplied to deposit a transparent conductive film having athickness of 950 nm and composed of fluorine-containing tin oxide(SnO₂:F) on the undercoating film at a film deposition rate of 8120nm/min.

This glass sheet had a haze ratio of 29% but did not show a whiteturbid, high-haze state. The reflectance, absorption coefficient, andsheet resistance thereof are collectively shown in Table 1 below.

Example 13

An undercoating film, a metal-containing thin film, and a transparentconductive film were formed on a glass ribbon in that order utilizing anonline CVD method. Specifically, 98 volume % of nitrogen and 2 volume %of hydrogen were supplied to the space inside the float bath so that thespace inside the float bath was kept at a slightly higher pressure thanthat outside the bath. While the inside of the bath was being kept to bea non-oxidizing atmosphere, a mixed gas composed of dimethyltindichloride (vapor), oxygen, nitrogen, and helium was supplied from thefirst coater located on the most upstream side to form a thin film(first undercoating layer) having a thickness of 35 nm and composed oftin oxide on the glass ribbon. Subsequently, a mixed gas composed ofmonosilane, ethylene, oxygen, and nitrogen was supplied from the secondcoater to form a thin film (second undercoating layer) having athickness of 25 nm and composed of silicon oxide on the firstundercoating layer. Further, a mixed gas composed of dimethyltindichloride (vapor), oxygen, water vapor, and nitrogen was supplied fromthe third coater to form a metal-containing thin film having a thicknessof 50 nm and composed of tin oxide (SnO₂) on the second undercoatinglayer having a surface temperature of 690° C. at a film deposition rateof 1250 nm/min. Further, using the coater installed on the furtherdownstream side, a mixed gas composed of tin tetrachloride (vapor),water vapor, nitrogen, helium, and hydrogen fluoride was supplied with aglass temperature of 630° C. to deposit a transparent conductive filmhaving a thickness of 740 nm and composed of fluorine-containing tinoxide (SnO₂:F) at a film deposition rate of 18500 nm/min.

This glass sheet had a haze ratio of 17% and did not show a whiteturbid, high-haze state. The reflectance, absorption coefficient, andsheet resistance thereof are shown in Table 1 below.

Example 14

A glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 13 except that the conditions werechanged as specified in the following. From the first coater, a mixedgas composed of tin tetrachloride (vapor), water vapor, nitrogen, andhelium was supplied to form a thin film (first undercoating layer)having a thickness of 45 nm and composed of tin oxide on the glassribbon. In addition, from the third coater, a mixed gas composed of tintetrachloride (vapor), oxygen, water vapor, and nitrogen was supplied toform a metal-containing thin film having a thickness of 90 nm andcomposed of tin oxide (SnO₂) on the undercoating film (secondundercoating layer) having a surface temperature of 680° C. at a filmdeposition rate of 1830 nm/min. Using the coater installed on thefurther downstream side, a transparent conductive film having athickness of 690 nm and composed of fluorine-containing tin oxide(SnO₂:F) was deposited with a glass temperature of 630° C. at a filmdeposition rate of 7030 nm/min.

This glass sheet had a haze ratio of 20% and did not show a whiteturbid, high-haze state. The reflectance, absorption coefficient, andsheet resistance thereof are shown in Table 1 below.

Example 15

A glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 14 except that the conditions werechanged as specified in the following. A metal-containing thin filmhaving a thickness of 140 nm and composed of tin oxide (SnO₂) was formedon the undercoating film at a film deposition rate of 2850 nm/min. Atransparent conductive film having a thickness of 636 nm and composed offluorine-containing tin oxide (SnO₂:F) was deposited at a filmdeposition rate of 6470 nm/min.

This glass sheet had a haze ratio of 27% and did not show a whiteturbid, high-haze state. The reflectance, absorption coefficient, andsheet resistance thereof are shown in Table 1 below.

Example 16

A glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 14 except that the conditions werechanged as specified in the following. A thin film (first undercoatinglayer) having a thickness of 80 nm and composed of tin oxide was formedon a glass ribbon. A transparent conductive film having a thickness of710 nm and composed of fluorine-containing tin oxide (SnO₂:F) wasdeposited on the metal-containing thin film at a film deposition rate of7220 nm/min.

This glass sheet had a haze ratio of 25% and did not show a whiteturbid, high-haze state. The reflectance, absorption coefficient, andsheet resistance thereof are shown in Table 1 below.

Example 17

A glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 14 except that the conditions werechanged as specified in the following. A transparent conductive filmhaving a thickness of 670 nm and composed of fluorine-containing tinoxide (SnO₂:F) was deposited on a metal-containing thin film at a filmdeposition rate of 6820 nm/min.

This glass sheet had a haze ratio of 16% and did not show a whiteturbid, high-haze state. The reflectance, absorption coefficient, andsheet resistance thereof are shown in Table 1 below.

Comparative Example 5

A glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 10 except that the conditions werechanged as specified in the following. Without forming the buffer layer(metal-containing thin film) on the undercoating film, a transparentconductive film composed of fluorine-containing tin oxide (SnO₂:F) wasdeposited directly.

This glass sheet on which the buffer layer was not formed showed such awhite turbid, high-haze state that an object behind the glass sheetcould not be recognized. For that reason, measurements of haze ratio,reflectance, absorption coefficient, and sheet resistance value were notcarried out.

Comparative Example 6

The glass sheet provided with a transparent conductive film was preparedin a similar manner to Example 13 except that the conditions werechanged as specified in the following. Without forming a buffer layer(metal-containing thin film) on the undercoating film, that is, with thesupply of the mixed gas being stopped for the third coater, atransparent conductive film having a thickness of 600 nm and composed offluorine-containing tin oxide (SnO₂:F) was deposited at a filmdeposition rate of 15000 nm/min.

This glass sheet on which the buffer layer was not formed showed such awhite turbid, high-haze state that an object behind the glass sheetcould not be recognized. For that reason, measurements of haze ratio,reflectance, absorption coefficient, and sheet resistance value were notcarried out.

Manufacturing Example 1

A thin film having a thickness of 0.3 μm and composed of amorphoussilicon was formed on each of the transparent conductive films depositedaccording to Examples 10, 11, 13 to 17, and Comparative Examples 5 and6, by a plasma CVD method using monosilane and hydrogen as rawmaterials. Thereafter, by electron beam vapor deposition, a thin film(back electrode) having a thickness of 300 nm composed of silver wasformed, and samples of photoelectric conversion elements were thusprepared. These samples are made in accordance with a generalconfiguration of a solar cell in which a thin film composed of amorphoussilicon serves as its photoelectric conversion layer. The photoelectricconversion efficiencies of these samples were measured using a knowntechnique, the results of which are collectively shown in Table 1 below.

Manufacturing Example 2

A thin film having a thickness of 2 μm and composed of crystallinesilicon was formed on each of the transparent conductive films depositedaccording to Examples 10, 11, and 13 as well as Comparative Examples 5to 6, by a plasma CVD method using monosilane and hydrogen as rawmaterials. Thereafter, by electron beam vapor deposition, a thin film(back electrode) having a thickness of 300 nm and composed of silver wasformed, and samples of photoelectric conversion elements were thusprepared. These samples are made according to a general configuration ofa solar cell in which a thin film composed of crystalline silicon servesas its photoelectric conversion layer. The photoelectric conversionefficiencies of these samples were measured using a known technique, andthe results are collectively shown in Table 1 below.

For the photoelectric conversion efficiencies of Comparative Examples 5and 6 in Manufacturing Examples 1 and 2, measurement of thephotoelectric conversion efficiencies was attempted, but almost noefficiency was obtained. This may be due to the fact that the p-, i-,and n-type thin films composed of amorphous silicon and the thin filmcomposed of crystalline silicon were not formed uniformly within thesurface because of the giant particles of tin oxide observed as whiteturbidity.

The comparison between Example 12 and Comparative Example 5 demonstratesthat when the film deposition rate for the buffer layer exceeds 600nm/min., the transparent conductive film forms a white turbidity. InExamples 13 to 17, the transparent conductive films did not cause awhite turbidity even though the film deposition rate for the bufferlayer greatly exceeds 1000 nm/min; this may be attributed to the factthat alkali-halogen particles were taken into the first undercoatinglayer during the formation of the first undercoating layer, ordisappeared because of the heat, and as a consequence the surface of theundercoating film became non-flat.

For reference purposes, a measurement was carried out to examine how theabsorption coefficient of a transparent conductive film changes when rawmaterials of the transparent conductive film were varied in theircontents of the compositional components (Reference Examples 2 to 4).

Reference Example 2

A glass sheet provided with a transparent conductive film was preparedin a similar manner to that in Example 14 except that the conditionswere changed as specified in the following. On the glass ribbon, a thinfilm (first undercoating layer) having a thickness of 35 nm and composedof tin oxide was formed. On the undercoating film (second undercoatinglayer), a metal-containing thin film having a thickness of 110 nm andcomposed of tin oxide (SnO₂) was formed at a film deposition rate of1550 nm/min. Further, a mixed gas composed of 1.8 mol % tintetrachloride (vapor), 57 mol % water vapor, nitrogen, and hydrogenfluoride was supplied to deposit a transparent conductive film having athickness of 504 nm and composed of fluorine-containing tin oxide(SnO₂:F) on the metal-containing thin film at a film deposition rate of3480 nm/min. This glass sheet had a haze ratio of 3.3% and showedabsorption coefficients of 0.53 at 400 nm, 0.36 at 500 nm, 0.26 at 600nm, and 0.24 at 700 nm.

Reference Example 3

A glass sheet provided with a transparent conductive film was preparedin a similar manner to that in Reference Example 2 except that theconditions were changed as specified in the following, and theabsorption coefficient thereof was measured. As a raw material of thetransparent conductive film, a mixed gas was used whose contents of thecompositional components were 1.8 mol % tin tetrachloride (vapor), 57mol % water vapor, 23 mol % oxygen, nitrogen, and hydrogen fluoride todeposit a transparent conductive film having a thickness of 500 nm andcomposed of fluorine-containing tin oxide (SnO₂:F) at a film depositionrate of 3450 nm/min. This glass sheet had a haze ratio of 3% and showedabsorption coefficients of 0.64 at 400 nm, 0.32 at 500 nm, 0.24 at 600nm, 0.17 at 700 nm.

Reference Example 4

A glass sheet provided with a transparent conductive film was preparedin a similar manner to that in Reference Example 2 except that theconditions were changed as specified in the following, and theabsorption coefficient thereof was measured. As a raw material of thetransparent conductive film, a mixed gas was used whose contents of thecompositional components were 1.8 mol % tin tetrachloride (vapor), 85.6mol % water vapor, nitrogen, and hydrogen fluoride to deposit atransparent conductive film having a thickness of 453 nm and composed offluorine-containing tin oxide (SnO₂:F) at a film deposition rate of 3120nm/min. This glass sheet had a haze ratio of 3.5% and showed absorptioncoefficients of 0.76 at 400 nm, 0.4 at 500 nm, 0.26 at 600 nm, 0.17 at700 nm.

The comparison between Reference Examples 1 to 3 demonstrates that whenthe content of the oxidizing material (oxygen or water vapor) in themixed gas of the raw material is higher, the absorption coefficientstoward long wavelengths reduce.

With the configurations described thus far, this invention exhibits thefollowing advantageous effects.

With a thin film-forming method according to this invention, thegeneration of giant crystal grains is suppressed even if the filmdeposition rate for the thin film containing a crystalline metal oxideas the main component is made faster. As a consequence, even when thethin film containing a crystalline metal oxide as the main component isformed on a transparent substrate at a high film deposition rate, whiteturbidity does not easily occur, and moreover, even when a functionalfilm is formed on the foregoing thin film, defects do not easily form.Therefore, the use of this thin film-forming method enables themanufacture of a substrate provided with a high quality thin filmcontaining a crystalline metal oxide as the main component to be highlyefficient. Moreover, since a substrate according to this invention has atransparent conductive film provided with relatively uniform and largesurface roughness, transmitted light and reflected light are scatteredeffectively; therefore, the light trapping effect is exhibitedeffectively. Furthermore, with its low reflectivity and low absorptioncoefficient, this transparent conductive film can increase theconversion efficiency in photoelectric conversion when used for aphotoelectric conversion device. TABLE 1 Example Example Example ExampleExample Example 10 11 12 13 14 15 Undercoating First Undercoating Layer— — — 35 45 45 Film Thickness (nm) Second Undercoating Layer 25 20 25 2525 25 Thickness (nm) Buffer Layer Thickness (nm) 30 100 50 50 90 140Deposition (° C.) 620 620 620 690 680 680 Temp. Film (nm/min.) 50 170510 1250 1830 2850 Deposition Rate Transparent Thickness (nm) 800 720950 740 690 636 Conductive Deposition (° C.) 620 620 620 630 630 630Film Temp. Film (nm/min.) 670 480 8120 18500 7030 6470 Deposition RateSubstrate Haze Ratio (%) 22 17 29 17 20 27 Characteristics Reflectivity(400-1100 nm 11.5 12.8 9.3 8.5 9.4 9.4 average) Absorption 400 (nm) 0.360.38 0.45 0.40 0.57 0.59 Coefficient 500 (nm) 0.36 0.37 0.37 0.39 0.400.51 (x10³ cm⁻¹) 600 (nm) 0.35 0.35 0.39 0.38 0.35 0.43 700 (nm) 0.350.36 0.57 0.38 0.38 0.47 Sheet (Ω/□) 10 13 10.4 15 10.6 9.2 ResistancePhotoelectric Photoelectric Amorphous 7.8 7.8 — 7.7 8.65 9.5 ConversionConversion Film Device Efficiency (%) Crystalline 7.3 7.2 — 7.1 — — Film(%) Example Example Comp. Comp. 16 17 Example 5 Example 6 UndercoatingFirst Undercoating Layer 80 45 — 35 Film Thickness (nm) SecondUndercoating Layer 25 25 25 25 Thickness (nm) Buffer Layer Thickness(nm) 90 90 — — Deposition (° C.) 680 680 — — Temp. Film (nm/min.) 18301830 — — Deposition Rate Transparent Thickness (nm) 710 670 800 600Conductive Deposition (° C.) 630 630 620 630 Film Temp. Film (nm/min.)7220 6820 670 15000 Deposition Rate Substrate Haze Ratio (%) 25 16 WhiteWhite Characteristics Turbidity Turbidity Reflectivity (400-1100 nm 11.09.4 — — average) Absorption 400 (nm) 0.65 0.56 — — Coefficient 500 (nm)0.51 0.42 — — (× 10³ cm⁻¹) 600 (nm) 0.44 0.36 — — 700 (nm) 0.45 0.37 — —Sheet (Ω/□) 10 13.2 — — Resistance Photoelectric Photoelectric Amorphous8.61 9.76 1.1 0.8 Conversion Conversion Film Device Efficiency (%)Crystalline — — 0.6 0.5 Film (%)

1. A thin film-forming method of forming a thin film containing acrystalline metal oxide as a main component on a substrate using athermal decomposition method, comprising: forming the thin film using araw material containing a chloride of a metal; and prior to the formingof the thin film, 1) disposing metal-containing particles on thesubstrate, or 2) forming, at a film deposition rate slower than a filmdeposition rate for the thin film, a metal-containing thin film on thesubstrate, wherein in the case of the step 2), the thin film containingthe metal oxide as the main component is formed directly on themetal-containing thin film.
 2. The thin film-forming method according toclaim 1, wherein the chloride of a metal is tetrachloride of a metal. 3.The thin film-forming method according to claim 1, wherein the rawmaterial includes water vapor.
 4. The thin film-forming method accordingto claim 1, wherein the film deposition rate for the thin filmcontaining a metal oxide as the main component is 3500 nm/min. orgreater.
 5. The thin film-forming method according to claim 1, whereinthe substrate is a glass ribbon in a float process, and the thin filmcontaining a metal oxide as the main component is formed in a floatbath.
 6. The thin film-forming method according to claim 1, wherein thesubstrate is a glass or a glass ribbon containing an alkaline component,and prior to the disposing of the metal-containing particles or theforming of the metal-containing thin film, an undercoating filmcontaining a silicon oxide as a main component is formed.
 7. The thinfilm-forming method according to claim 6, wherein a surface of theundercoating film is not flat.
 8. The thin film-forming method accordingto claim 7, wherein the film deposition rate for the thin filmcontaining a metal oxide as the main component is 6300 nm/min. orgreater.
 9. A substrate comprising, in that order, a buffer layer havinga film thickness of 250 nm or less, and a transparent conductive filmdeposited by a thermal decomposition method using a tin chloride as araw material.
 10. The substrate according to claim 9, wherein thetransparent conductive film has an absorption coefficient of 1×10³ cm⁻¹or less in a wavelength range of 400 to 700 nm, the maximum value of theabsorption coefficient being 1.7 times or less of the minimum valuethereof, and a sheet resistance of 15 Ω/□ or less.
 11. The substrateaccording to claim 9, further comprising: a undercoating film interposedbetween the substrate and the buffer layer, the undercoating filmcomprising: a first undercoating layer having a refractive index of 1.6to 2.5 and a thickness of 5 to 100 nm, and a second undercoating layerhaving a refractive index of 1.4 to 2.0 and a thickness of 5 to 100 nm.12. The substrate according to claim 11, wherein a surface of theundercoating film is not flat.
 13. The substrate according to claim 9,wherein the transparent conductive film has a film thickness of 1000 nmor less and a haze ratio of 12% or greater.
 14. A photoelectricconversion device comprising the substrate according to claim 9.